Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
An image forming apparatus typified by a multi-functional peripheral reads an image of a document using an image reading unit, subsequently irradiates a photoreceptor, which is included in an image forming unit, with light based on the read image to form an electrostatic latent image on the photoreceptor. Then, the image forming apparatus supplies charged toners on the formed electrostatic latent image to form a visible image, and subsequently transfers the toner to be fixed on a paper sheet, and outputs it outside the apparatus.
Here, there are proposed techniques on a fixing unit that is included in an image forming apparatus and fixes toner on a paper sheet.
One of the above-described fixing unit includes: a roller that fixes an image on a paper sheet; a plurality of heaters that are located inside the roller and configured such that a distribution of an amount of supplied heat differs in a longitudinal direction of the roller; a temperature detecting unit that detects temperatures of the roller; and a control unit that performs an energization control of the heater by a pattern of a half-wave period of an AC power supply based on a detection result detected by the temperature detecting unit. The control unit has a feature that when the temperature detecting unit detects that a temperature of an end portion of the roller in the longitudinal direction is lower than a set target temperature, the control unit performs a full energization control to the heater having the largest amount of supplied heat at its end portion among the plurality of heaters and also performs the energization control on the heater having the next largest amount of supplied heat at its end portion among the plurality of heaters by a pattern of a predetermined duty ratio, or performs the energization control on the heater having the largest amount of supplied heat at its end portion among the plurality of heaters by the pattern of the predetermined duty ratio and also performs the energization control by turning off the heater having the next largest amount of supplied heat at its end portion among the plurality of heaters.
Another of the above-described image forming apparatus includes: a fixing roller that heats and fixes a toner image on a paper sheet; a first heater that is located to heat the fixing roller and has a heat generation amount at one end portion of the fixing roller in an axial direction larger than that of the other end portion; a second heater that has a heat generation amount at the other end portion larger than that of the one end portion; a temperature sensor that detects the temperatures of the fixing roller; and a control unit that determines an energization ratio of the first heater and the second heater such that the temperature detected by the temperature sensor becomes equal to a target temperature to control energization and non-energization of the first heater and the second heater by the energization ratio, and also obtains a temperature gradient value of the fixing roller in the axial direction generated by the energization of the first heater and/or the energization of the second heater and non-energization of both the first heater and the second heater, and then causes the heater that decreases the temperature gradient value to be preferentially energized.